Existing water pump pliers have the common characteristic of jaws offset at an angle to the pliers' handles and a pivot post, in the form of a bolt or rivet, mounted in the area rearward of the jaw on one of the handles and projecting through an elongate slot on the other handle. In such pliers, means for enabling selective spacing of the distance between the jaws may take the form of spaced apart ridges or teeth provided along the inside long edge of the slot and adapted for incremental selective binding engagement with the pivot post. Another well known way of providing distance adjustment between the jaws in such pliers is to provide spaced apart arcuate ridges on the facing surfaces of the slot for engagement by the pivot post. All such tools require a two-handed operation to adjust the jaw spacing the size of a workpiece to be gripped between the jaws. This adjustment involves pulling the handles apart to permit the pivot post to slide along the slot to move the movable one of the jaws to a position that provides a jaw spacing approximating to the size of the workpiece that is to be gripped.
Other known types of pliers are adapted to slideably close upon a workpiece in response to manual closing of the handles and, in response to contact with the workpiece, automatically lock against further sliding action by engaging suitable teeth and thereby shift from a sliding to a pivoting mode whereby continued exertion of manual force on the handles increases the gripping action upon the workpiece.
The gripping action of the known pliers is a function of the relationship between the length of the operating handles and the length of the jaws from the pivot post, which is typically in a ratio of around 5:1. The result is that a considerable portion of the torque applied to the operating handles is required to grip the workpiece, meaning there is often insufficient torque available to shift a tight workpiece.
In certain circumstances it would be a considerable advantage to be able to lock pliers upon a workpiece. The known pliers are unable to include this function.
Another drawback of the known pliers is that the pivot post fixing action, whether by spaced apart ridges, teeth or arcuate ridges in the slot, is such that the jaws/handles are seldom in an optimum position prior to the shift from sliding to a pivoting mode. This results in a variable gripping action upon the workpiece.